1. Field of the Invention
The present invention concerns a device, generally known as a "pitch detector" for determining the basic period of speech, and more particularly a device creating marking impulses corresponding to significant peaks in a speech signal.
2. Description of the Prior Art
In the U.S. Pat. No. 3,852,535, granted Dec. 12, 1974, there has been described a device for measuring the fundamental period or pitch of a speech signal. This device comprises essentially a processor of an analogue speech signal, a voicing or unvoicing detector, a circuit for detecting significant peaks of the previously treated speech signal giving pitch impulses coinciding with the significant peaks, and means for processing the said impulses.
The detection of the significant positive and negative peaks in a speech signal is generally effected, in particular in the device for measuring the fundamental period of a speech signal which is the subject of the aforesaid patent, by storing in an integrator the peak amplitudes and by applying to a comparator on the one hand the previously treated speech signal and on the other hand the output signal of the integrator which is a decreasing exponential signal departing from the amplitude of the stored peak. When the amplitude of a new peak of the speech signal and the amplitude of the decreasing exponential signal become equal the comparator delivers a pitch impulse.
The time constant of the decreasing exponential must be suitably regulated for the detection circuit to deliver only one pitch impulse, or two if need be, per pitch period. In the aforementioned patent this objective was approached by adding to the decreasing exponential signal a calibrated part of the speech signal.